BACKUP BATTERY SYSTEM

A backup battery system includes a charging-discharging module and a battery module. The charging-discharging module includes a first connector and a first engaging member. The battery module is detachably connected to the charging-discharging module and includes a second connector corresponding to the first connector and a second engaging member corresponding to the first engaging member. When the battery module is connected to the charging-discharging module, the first connector is joined with the second connector and the first engaging member is fixed to the second engaging member.